Ignore SocketExceptions when shutting down

Author: michaelklishin

projects/client/RabbitMQ.Client/src/client/impl/ConnectionBase.cs

@@ -665,7 +665,15 @@ public void MainLoop()
                 // connection closes.
                 if (shutdownCleanly)
                 {
-                    ClosingLoop();
+                    try
+                    {
+                        ClosingLoop();
+                    } catch (SocketException se)
+                    {
+                        // means that socket was closed when frame handler
+                        // attempted to use it. Since we are shutting down,
+                        // ignore it.
+                    }
                 }
 
                 FinishClose();